中国大陆科学钻探主孔100～2000m岩心的磁化率各向异性及其地质意义  

Anisotropy of magnetic susceptibility of the cores from the mainhole (100-2000m) of the Chinese Continental Scientific Drilling: Implications for the ultrahigh-pressure ( UHP) metamorphic rocks.

作　　者：徐海军[1] 金振民[2] 欧新功[3] 

机构地区：[1]中国地质大学研究生院,武汉430074 [2]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [3]中国科学院广州地球化学研究所,广州510640

出　　处：《岩石学报》2006年第7期2081-2088,共8页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2003CB716506);国家重大科学工程项目"中国大陆科学钻探工程".

摘　　要：在常温常压条件下获得了中国大陆科学钻探(CCSD)主孔331块岩心的磁化率各向异性(AMS)数据,并建立了主孔100—2000m的体积磁化率和AMS连续剖面。数据统计分析显示,主孔100—2000m岩心的磁化率(κ)介于1．05×10-4SI和0．12SI之间,几何平均值为1．855×10-3SI;磁化率各向异性度(Pj)介于1．04和2．10之间,几何平均值为1．155。该井段出露的主要岩石类型有榴辉岩、退变质榴辉岩、角闪岩、正片麻岩、副片麻岩和蛇纹石化橄榄岩,它们的垂向分布特征控制着磁化率剖面的变化。主孔的超高压变质岩石在折返过程中普遍经历了强烈的角闪岩相退变质作用的改造。其磁化率特征也发生相应的改变。蛇纹石化橄榄岩具有很高的磁化率(8．58×10-2SI)和各向异性度(1．335)。这主要源于橄榄岩蛇纹石化过程中产生的大量磁铁矿。榴辉岩、退变质榴辉岩和角闪岩代表榴辉岩从新鲜到完全退变质的三个阶段,它们的磁化率和磁化率各向异性度分别为榴辉岩(1．28×10-3SI、1．077)、退变质榴辉岩(3．19×10-3SI、1．206)、角闪岩(1．02×10-3SI、1．104)。正片麻岩的磁化率和各向异性度分别为5．34×10-3SI和1．167。副片麻岩的磁化率和各向异性度分别为3．46×10-4SI和1．150。对58个变形岩石的AMS测试结果显示,其磁化率椭球体的主轴方向与岩石组构基本一致,即最大磁化率主轴κ1平行矿物线理,最小磁化率主轴κ3垂直岩石面理。同时,这些变形岩石的AMS椭球体多呈现明显的压扁状特征,反映超高压变质岩石在折返过程中处于强烈挤压变形的构造应力环境,为苏鲁超高压变质板片的挤出折返模式提供了佐证。该研究成果也为超高压变质岩石地区磁学研究、地球物理调查和测井成果的解释提供了重要的实验约束。The anisotropies of magnetic susceptibility of 331 samples from the 100- 2000m main hole of the Chinese Continental Scientific Drilling Project （CCSD） have been measured in the conditions of room temperature and pressure. The vertical profiles of the bulk magnetic susceptibility and its anisotropy （AMS） parameters from 100m to 2000m were constructed. The experimental data suggest that the bulk magnetic susceptibility vary from 1.05 × 10^-4SI to 0.12SI with the geometric mean value of 1. 855 × 10^-3SI, and the anisotropy degree Pj varies from 1.04 to 2.01 with the geometric mean value of 1. 155. The ultrahigh-pressure （UHP） metamorphic rocks （eclogite, retrograded eclogite, amphibolite, orthogneiss, paragneiss and serpentinized peridotite） are the rock types most frequently found down to a depth of 2000m. And the vertical profiles show that the magnetic susceptibility changes with different types of the UHP metamorphic rocks at different depth. Nearly all the analyzed drill cores from the CCSD 100 - 2000m main hole were overprinted by amphibolite facies retrograde metamorphism in the process of exhumation of the UHP slab, and the retrogression put an important influence on the rock magnetic susceptibility. The serpentinized peridotites have very high values of magnetic susceptibility （8.58 × 10^-2SI） and anisotropy degree （1. 335 ）, which are mainly attributed to the formation of magnetite during serpentinization of peridotite. The eclogites can be divided into fresh eclogites, retrograded eclogites and amphibolites according to their degrees of retrogression. It is clear that the retrograded eclogites have relatively high magnetic susceptibility （3.19 × 10^-SSI） and high anisotropy degree （ 1. 206） comparing with the fresh eclogites （ κ= 1.28 × 10^-3 SI, Pj = 1. 077 ） and amphibolites （ κ= 1.02 × 10^-3 SI, Pj = 1. 104）. The orthogneiss has high value of magnetic susceptibility （5.34 × 10^-3 SI） and anisotropy degree （1. 167）, while the paragneiss has relati

关 键 词：磁化率各向异性 超高压变质岩石 中国大陆科学钻探 

分 类 号：P318.4[天文地球—固体地球物理学] P588.346[天文地球—地球物理学]